http://www.techonthenet.com/oracle/functions/to_char.php
http://hi.baidu.com/djx_5211314/blog/item/4fec8713905df5826438db47.html
In Oracle/PLSQL,
the to_char function converts a number or date to a string.
The syntax for the to_char function is:
to_char( value, [ format_mask ], [ nls_language ] )
value can either be a number or date that will be converted to a string.
format_mask is optional. This is the format that will be used to convert value to a string.
nls_language is optional. This is the nls language used to convert value to a string.
Applies To:
Oracle 8i, Oracle 9i, Oracle 10g, Oracle 11g
Examples - Numbers
The following are number examples for the to_char function.
to_char(1210.73, '9999.9') would return '1210.7'
to_char(1210.73, '9,999.99') would return '1,210.73'
to_char(1210.73, '$9,999.00') would return '$1,210.73'
to_char(21, '000099') would return '000021'
Examples - Dates
The following is a list of valid parameters when the to_char function is used to convert a date to a string. These parameters can be used in many combinations.
The following are date examples for the to_char function.
to_char(sysdate, 'yyyy/mm/dd'); would return '2003/07/09'
to_char(sysdate, 'Month DD, YYYY'); would return 'July 09, 2003'
to_char(sysdate, 'FMMonth DD, YYYY'); would return 'July 9, 2003'
to_char(sysdate, 'MON DDth, YYYY'); would return 'JUL 09TH, 2003'
to_char(sysdate, 'FMMON DDth, YYYY'); would return 'JUL 9TH, 2003'
to_char(sysdate, 'FMMon ddth, YYYY'); would return 'Jul 9th, 2003'
You will notice that in some examples, the format_mask parameter begins with "FM". This means that zeros and blanks are suppressed. This can be seen in the examples below.
to_char(sysdate, 'FMMonth DD, YYYY'); would return 'July 9, 2003'
to_char(sysdate, 'FMMON DDth, YYYY'); would return 'JUL 9TH, 2003'
to_char(sysdate, 'FMMon ddth, YYYY'); would return 'Jul 9th, 2003'
The zeros have been suppressed so that the day component shows as "9" as opposed to "09".